Improvement of nutritive value of guar meal through reduction of viscosity by enzyme supplementation

Abstract

Guar meal is a high protein by-product of guar gum production that contains a residual gum, galactomannan polysaccharide. The gum increases intestinal viscosity while decreasing nutrient absorption. Four experiments examined effects of two guar meal fractions (hull and germ) and β-mannanase on in vitro feed viscosity, and on in vivo growth performance and intestinal viscosity in chickens. In vitro feed viscosity was measured at several β-mannanase concentrations in corn/soy diets containing 0, 2.5, 5.0, 7.5, 10.0% guar meal. The enzyme significantly reduced supernatant viscosity of extracts from guar meal containing feeds except for the 2.5% germ fraction diet. In Experiment 2, 360 day-old chicks were randomly fed diets containing 0, 2.5, 5.0, 7.5 or 10.0% guar hull or germ fractions. At 20 days, three birds per replicate were weighed, and organs were excised and weighed. Intestinal contents from duodenum, jejunum, and ileum were pooled within replicate for intestinal viscosity determination. In Experiments 3 and 4, 324 day-old chicks were fed 0, 5.0, or 7.5% guar germ fraction, or 0, 2.5%, and 5.0% hull fraction with β-mannanase. Body weight and feed consumption were recorded weekly. At 21 days, three chicks per replicate were eviscerated, weighed, and digesta viscosity determined. The hull, but not the germ, fraction significantly depressed body weight. Feed conversion was not significantly affected until more than 7.5% guar germ fraction or 5.0% guar hull fraction was fed. Intestinal viscosity significantly increased at 7.5% germ and at 2.5% hull fractions. The recommended enzyme concentration added to the 7.5% germ fraction diet reduced ileal viscosity from 5.05 to 2.35 centipoise, and enzyme significantly reduced ileal viscosity, increased body weight, and improved feed conversion of hull fraction diets. In summary, up to 7.5% guar meal germ fraction was fed to chickens to three weeks of age without growth depression or increased feed conversion. Hull fraction of guar meal depressed growth at as low as 2.5% of the diet, while b-mannanase improved growth and feed conversion to control levels. Guar meal increased intestinal viscosity and β-mannanase reduced guar meal-induced viscosity with a concomitant improvement of growth and feed conversion.